1. Field of the Invention
This invention relates to a method for treating urinary obstruction.
More particularly, it is concerned with a method for treating urinary obstruction which comprises administering a therapeutically effective amount of 6-[[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]amino]-1,3-dimethyluracil (also referred to as urapidil) or a pharmaceutically acceptable acid addition salt thereof to a mammal including a human being afflicted with urinary obstruction.
2. Description of the Prior Art
Urinary obstruction includes such symptoms as difficulty in urination, pollakiuria, nocturnal enuresis, incontinence of urine, feeling of residual urine and acute ischuria. These symptoms occur due to a variety of causes, for example, hypertrophy of prostate glands, autonomic imbalance, organic deficiencies of the urinary tracts or nephritis and cystitis caused by infectious microorganisms.
It has been revealed that the urinary obstruction caused by hypertonia of the sympathetic nervous system and prostatauxe among those mentioned above is deeply related to the contraction of smooth muscles via .alpha..sub.1 -adrenoceptors (for example, Yamaguchi et al.: Iyaku Journal, Vol. 24, No. 12, 1988, p. 2661).
As for hypertrophy of the prostate glands in humans, it is suggested that increase in distribution density of .alpha..sub.1 -adrenoceptors promotes resistance to urination, because there is observed no change of the sensitivity of .alpha..sub.1 -adrenoceptors in the prostate glands but marked increase in their distribution density in proportion to hypertrophy of the prostate glands (Yokoyama et al.: Nihon Hinyoki Gakkai-shi, Vol. 76, pp. 325-327, 1985).
Further, efficacy of prazosin which has already been used as an .alpha..sub.1 -adrenoceptor blocking agent in antihypertensives is clinically evaluated and is being recognized as a therapeutic agent for the urinary obstruction caused by hypertrophy of prostate glands or hypertonia of the sympathetic nervous system (Yamaguchi et al.: Iyaku to Yakugaku, Vol. 19, pp. 411-429, 1988).
Furthermore, certain prazosin-analogous compounds which exhibit a mild antihypertensive action (Japanese Patent Publication No. 40229/1986) have been found to possess an .alpha..sub.1 -adrenoceptor blocking activity at those sites which play an important role in urination mechanism, and it is proposed that they will be useful not only as a hypotensive agent but also as a therapeutic agent for urinary obstruction (Japanese Patent LOP Publication No. 26517/1989).
However, since these .alpha..sub.1 -adrenoceptor blocking agents are poorly selective in that they block not only .alpha..sub.1 -adrenoceptors in tissues of the urinary tracts which play an important role in urination mechanism but also .alpha..sub.1 -adrenoceptors distributed in blood vessels, there still remain problems of side effects such as orthostatic hypotensive asthenia. Thus, a therapeutic agent without such side effects is demanded. Particularly, .alpha..sub.1 -adrenoceptor blocking agents which are less active on the .alpha..sub.1 -adrenoceptors distributed in blood vessels but highly active on the .alpha..sub.1 -adrenoceptors distributed in the lower urinary tracts, for example, the prostate gland, internal urethral sphicter muscle and trigonum vesicae, would be useful as agents for treating urinary obstruction without fear of said side effects. In this respect, it is a subject to develop, as a therapeutic agent for urinary obstruction, .alpha..sub.1 -adrenoceptor blocking agents possessing such properties.